CALGreen · California Green Building Standards Code (CALGreen)
How does site grading/drainage affect water management and groundwater recharge?
CALGreen requires that construction plans show how finished grading and drainage will keep surface water from entering buildings (§ 4.106.3). Practical solutions include swales, French drains, retention gardens, cisterns, or other measures that both divert flows from foundations and, when feasible, infiltrate or store water to support groundwater recharge; projects disturbing soil must also manage stormwater during construction (§ 4.106.2), and Appendix guidance (A5.106.3) recommends Low Impact Development strategies to mitigate the 85th‑percentile rainfall event.
Last reviewed: July 6, 2026
What the code requires — in plain English
Construction plans must show how site grading or the drainage system will manage all surface water so water does not enter buildings. The code lists acceptable methods (for example swales, water collection/disposal systems, French drains, water retention gardens) and explicitly calls out that measures that keep surface water away from buildings and aid in groundwater recharge are permitted. See § 4.106.3.
The most important rule: show on the plans how grading/drainage routes surface water away from foundations and, when feasible, use measures that allow infiltration or storage to support groundwater recharge.
Requirements in detail
Core obligation
- Show, on the construction documents, how site grading or a drainage system will manage all surface water flows to keep water from entering buildings. This is the controlling requirement: § 4.106.3.
Examples of acceptable methods (the code lists these as examples)
- Swales
- Water collection and disposal systems (e.g., cisterns, rain barrels)
- French drains
- Water retention gardens (bioretention/rain gardens)
- “Other water measures which keep surface water away from buildings and aid in groundwater recharge.”
All of the above are explicitly named in § 4.106.3.
Construction-stage stormwater requirement (related)
- Projects that disturb less than one acre (and are not part of a larger plan that totals one acre or more) must still provide measures to manage storm water during construction (retention basins, filters, wattles, or compliance with local ordinance). See § 4.106.2. One acre is the key threshold for reporting/permit differences.
Low Impact Development (LID) — voluntary / Appendix guidance that impacts groundwater recharge design
- Appendix guidance requires new projects to mitigate (infiltrate, filter, or treat) stormwater runoff from the 85th-percentile 24‑hour runoff event (for volume-based BMPs) or the equivalent flow-based runoff and to employ at least two LID methods (bioretention, cisterns, green roofs, impervious-area disconnection, permeable paving, vegetative swales, etc.). See § A5.106.3.
- For greyfield or infill sites, Appendix A5 requires managing 40 percent of the average annual rainfall on the site’s impervious surfaces by infiltration, reuse, or evapotranspiration. See § A5.106.3.2.
Decision-relevant dimensions / values
| Decision factor | Key dimension / value | Why it matters | Code Reference |
|---|---|---|---|
| Construction disturbance threshold | 1 acre (disturbed soil) | Determines whether small‑site construction stormwater provisions apply and when NPDES permits may be required | § 4.106.2 |
| Required plan content | Show how all surface water flows are managed to prevent water entering buildings | Drives what must appear on construction documents (grading plan, drainage paths, BMPs) | § 4.106.3 |
| Acceptable LID target (Appendix) | 85th‑percentile 24‑hour runoff event (volume‑based) and use ≥ 2 LID methods | Establishes performance target for post‑construction runoff mitigation (Appendix guidance) | § A5.106.3 |
| Greyfield/infill target (Appendix) | 40% of average annual rainfall on impervious surfaces | Specific target for previously developed/infill sites to retain/regenerate rainfall | § A5.106.3.2 |
| Examples of compliance measures | Swales, French drains, water retention gardens, cisterns, porous paving | Practical tools that both keep water away from foundations and enable infiltration/reuse | § 4.106.3, § A5.106.3 |
Exceptions & special cases
Exception in § 4.106.3: additions and alterations that do not alter the drainage path are not required to re-document grading/drainage under this section. You must show that the drainage path remains unchanged. § 4.106.3.
Projects that disturb one acre or more, or that are part of a larger common plan totaling one acre or more, are subject to state construction stormwater permits (NPDES). The CALGreen note points designers to the State Water Resources Control Board for those larger projects (see § 4.106.2 and accompanying Note).
Appendix LID guidance is an implementation-level (Appendix A5) expectation for mitigation performance; local jurisdictions or the Regional Water Quality Control Board may have stricter or directly enforced LID/permit requirements (coordinate as applicable). § A5.106.3.
If the document set you provided does not include a local ordinance, the code text (files) does not specify local numeric rainfall depths or jurisdiction‑specific sizing standards — those must come from local stormwater rules or the Regional Water Board.
Common mistakes
- Not showing the actual flow paths or finished grades on the plans — CALGreen requires plans to indicate how all surface water flows are managed (§ 4.106.3). Omitting flow arrows/swale profiles is common but not acceptable.
- Treating LID measures only as landscaping extras rather than as required stormwater control features — Appendix guidance expects mitigation of the 85th‑percentile event and use of at least two LID strategies when applicable (§ A5.106.3).
- Failing to coordinate construction‑stage controls when disturbing soil — even sites under one acre must manage stormwater during construction under § 4.106.2.
- Designing retention/infiltration features without checking groundwater depth or local restrictions — the code and related plumbing/building rules require checking other applicable limitations (e.g., local NPDES, permitting, or Appendix constraints). The CALGreen materials point to the State Water Resources Control Board for larger disturbances.
Worked example — applying the rules with numbers (illustrative)
Note: CALGreen § 4.106.3 requires showing how surface water is managed but does not prescribe a single sizing method or specific rainfall depths in the section text. Appendix A5.106.3 sets performance targets (85th‑percentile runoff) but the exact rainfall depth is location‑dependent. The example below uses an assumed rainfall value for illustration; check local rainfall statistics and local LID sizing guidance for permit‑grade design.
Scenario:
- Lot area: 0.25 acre = 10,890 ft²
- Impervious area (driveway + roof + patio): 40% → 4,356 ft² (a common infill metric)
- Assumed 85th‑percentile 24‑hr rainfall (example only): 0.75 in = 0.0625 ft
Runoff volume to mitigate (volume = area × depth):
- Volume = 4,356 ft² × 0.0625 ft = 272.25 ft³ ≈ 2,036 gallons (1 ft³ ≈ 7.48 gal)
Design approach to meet CALGreen expectations:
- Show on the grading/drainage plan the flow paths from roofs and pavements to the proposed BMPs (required by § 4.106.3).
- Use at least two LID methods (Appendix guidance): e.g., disconnect roof leaders into a water retention garden (bioretention/rain garden) and route driveway runoff to a permeable paver area or an on‑site cistern for reuse. § A5.106.3.
- Size the rain garden for the example volume: if planting bed maximum drawdown depth = 1 ft, required footprint ≈ 272 ft² (~16 ft × 17 ft) to capture the event (this is an illustrative calculation; final sizing must use soil infiltration rates, ponding depth, and local guidance). Appendix guidance expects mitigation of the 85th‑percentile event via infiltration/reuse/filtering.
- Document the finished grades, swale slopes, overflow paths, and maintenance notes on the plans to demonstrate compliance with § 4.106.3.
Related CALGreen provisions
- § 4.106.2 — Storm water drainage and retention during construction (projects disturbing < 1 acre must manage stormwater during construction).
- § 4.106.3 — Grading and paving (controlling section for showing how grading/drainage manages surface water).
- § A5.106.3 — Low Impact Development (Appendix guidance: mitigate runoff from the 85th‑percentile event; use ≥ 2 LID methods).
- § A5.106.3.2 — Greyfield/infill sites: manage 40% of average annual rainfall on impervious surfaces.
Code references
Grounded in the retrieved California Green Building Standards Code (CALGreen) — click a citation to read the verbatim passage:
CALGreen § 4.106.3 High relevance — show source text
(Website: https://www.waterboards.ca.gov/water_issues/programs/stormwater/construction.html)
4.106.3 Grading and paving. Construction plans shall indicate how the site grading or drainage system will manage all surface water flows to keep water from entering buildings. Examples of methods to manage surface water include, but are not limited to, the following:
Swales
Water collection and disposal systems
French drains
Water retention gardens
Other water measures which keep surface water away from buildings and aid in groundwater recharge.
Exception: Additions and alterations not altering the drainage path.
4.106.4 Electric vehicle (EV) charging for new construction. New construction shall comply with Section 4.106.4.1 or 4.106.4.2. Electric vehicle supply equipment (EVSE) shall comply with the California Electrical Code.
Exceptions:
- On a case-by-case basis, where the local enforcing agency has determined EV charging and infrastructure are not feasible based upon one or more of the following conditions: 1.1. Where there is no local utility power supply or the local utility is unable to supply adequate power.
2025 CALIFORNIA GREEN BUILDING STANDARDS CODE 4-3
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RESIDENTIAL MANDATORY MEASURES
1.2. Where there is evidence suitable to the local enforcing agency substantiating that additional local utility infrastructure design requirements, directly related to the implementation of Section 4.106.4, may adversely impact the construction cost of the project. 2. Accessory Dwelling Units (ADU) and Junior Accessory Dwelling Units (JADU) without additional parking facilities.
4.106.4.1 New one- and two-family dwellings and townhouses with attached private garages. For each dwelling unit, install a listed raceway to accommodate a dedicated 208/240-volt branch circuit. The raceway shall not be less than trade size 1 (nominal 1-inch inside diameter). The raceway shall originate at the main service or subpanel and shall terminate into a listed cabinet, box or other enclosure in close proximity to the proposed location of an EV charger. Raceways are required to be continuous at enclosed, inaccessible or concealed areas and spaces. The service panel and/or subpanel shall provide capacity to install a 40-ampere 208/240-volt minimum dedicated branch circuit and space(s) reserved to permit installation of a branch circuit overcurrent protective device.
Exception: A raceway is not required if a minimum 40-ampere 208/240-volt dedicated EV branch circuit is installed in close proximity to the proposed location of an EV charger at the time of original construction in accordance with the California Elec- trical Code .
4.106.4.1.1 Identification. The service panel or subpanel circuit directory shall identify the overcurrent protective device space(s) reserved for future EV charging as “EV CAPABLE”. The raceway termination location shall be permanently and visibly marked as “EV CAPABLE”.
CALGreen § 4-1 High relevance — show source text
The state agency does not adopt sections identified by the following symbol: †.
2025 CALIFORNIA GREEN BUILDING STANDARDS CODE 4-1
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4-2 2025 CALIFORNIA GREEN BUILDING STANDARDS CODE
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4 RESIDENTIAL MANDATORY MEASURES
DIVISION 4.1 – PLANNING AND DESIGN
SECTION 4.101—GENERAL
4.101.1 Scope. The provisions of this division outline planning, design and development methods that include environmentally responsible site selection, building design, building siting and development to protect, restore and enhance the environmental quality of the site and respect the integrity of adjacent properties.
SECTION 4.102—DEFINITIONS
4.102.1 Definitions. The following terms are defined in Chapter 2.
FRENCH DRAIN.
WATTLES.
SECTION 4.103—SITE SELECTION (RESERVED)
SECTION 4.104—SITE PRESERVATION (RESERVED)
SECTION 4.105—DECONSTRUCTION AND REUSE OF EXISTING STRUCTURES (RESERVED)
SECTION 4.106—SITE DEVELOPMENT
4.106.1 General. Preservation and use of available natural resources shall be accomplished through evaluation and careful planning to minimize negative effects on the site and adjacent areas. Preservation of slopes, management of storm water drainage and erosion controls shall comply with this section.
4.106.2 Storm water drainage and retention during construction. Projects which disturb less than one acre of soil and are not part of a larger common plan of development which in total disturbs one acre or more, shall manage storm water drainage during construction. In order to manage storm water drainage during construction, one or more of the following measures shall be implemented to prevent flooding of adjacent property, prevent erosion and retain soil runoff on the site.
Retention basins of sufficient size shall be utilized to retain storm water on the site.
Where storm water is conveyed to a public drainage system, collection point, gutter or similar disposal method, water shall be filtered by use of a barrier system, wattle or other method approved by the enforcing agency.
Compliance with a lawfully enacted storm water management ordinance.
Note: Refer to the State Water Resources Control Board for projects which disturb one acre or more of soil, or are part of a larger common plan of development which in total disturbs one acre or more of soil.
(Website: https://www.waterboards.ca.gov/water_issues/programs/stormwater/construction.html)
4.106.3 Grading and paving. Construction plans shall indicate how the site grading or drainage system will manage all surface water flows to keep water from entering buildings. Examples of methods to manage surface water include, but are not limited to, the following:
Swales
Water collection and disposal systems
French drains
Water retention gardens
Other water measures which keep surface water away from buildings and aid in groundwater recharge.
Exception: Additions and alterations not altering the drainage path.
CALGreen § 5.106.9 High relevance — show source text
General lighting luminaires in areas such as outdoor parking, sales or storage lots shall meet these reduced ratings. Decorative luminaires located in these areas shall meet_U_-
value limits for “all other outdoor lighting.”|1. IESNA Lighting Zones 0 are not applicable; refer to Lighting Zones as defined in the_California Energy Code_ and Chapter 10 of the_California Administrative Code.
2. For property lines that abut public walkways, bikeways, plazas and parking lots, the property line may be considered to be 5 feet beyond the actual property line for purpose
of determining compliance with this section. For property lines that abut public roadways and public transit corridors, the property line may be considered to be the center-
line of the public roadway or public transit corridor for the purpose of determining compliance with this section.
3. General lighting luminaires in areas such as outdoor parking, sales or storage lots shall meet these reduced ratings. Decorative luminaires located in these areas shall meet_U-
value limits for “all other outdoor lighting.”|5.106.9 Reserved.
5.106.10 Grading and paving. Construction plans shall indicate how site grading or a drainage system will manage all surface water flows to keep water from entering buildings. Examples of methods to manage surface water include, but are not limited to, the following:
Swales.
Water collection and disposal systems.
French drains.
Water retention gardens.
Other water measures which keep surface water away from buildings and aid in groundwater recharge.
Exception: Additions and alterations not altering the drainage path.
5.106.11 Reserved.
5.106.12 Shade trees. [DSA-SS] Shade trees shall be planted to comply with Sections 5.106.12.1, 5.106.12.2 and 5.106.12.3. Percentages shown shall be measured at noon on the summer solstice. Landscape irrigation necessary to establish and maintain tree health shall comply with Section 5.304.6.
5.106.12.1 Surface parking areas. Shade tree plantings, minimum No. 10 container size or equal, shall be installed to provide shade over 50 percent of the parking area within 15 years.
Exceptions: Surface parking area covered by solar photovoltaic shade structures or shade structures with roofing materials that comply with Table A5.106.11.2.2 in Appendix A5 shall be permitted in whole or in part in lieu of shade tree plantings.
5.106.12.2 Landscape areas. Shade tree plantings, minimum No. 10 container size or equal shall be installed to provide shade of 20% of the landscape area within 15 years.
Exception: Playfields for organized sport activity are not included in the total area calculation.
5.106.12.3 Hardscape areas. Shade tree plantings, minimum No. 10 container size or equal shall be installed to provide shade over 20 percent of the hardscape area within 15 years.
Exceptions:
- Walks, hardscape areas covered by solar photovoltaic shade structures or shade structures with roofing materials that comply with Table A5.106.11.2.2 in Appendix A5 shall be permitted in whole or in part in lieu of shade tree plantings.
- Designated and marked play areas of organized sport activity are not included in the total area calculation.
2025 CALIFORNIA GREEN BUILDING STANDARDS CODE 5-11
CALGreen § 5.106.9 High relevance — show source text
Decorative luminaires located in these areas shall meet_U_-
value limits for “all other outdoor lighting.”|1. IESNA Lighting Zones 0 are not applicable; refer to Lighting Zones as defined in the_California Energy Code_ and Chapter 10 of the_California Administrative Code.
2. For property lines that abut public walkways, bikeways, plazas and parking lots, the property line may be considered to be 5 feet beyond the actual property line for purpose
of determining compliance with this section. For property lines that abut public roadways and public transit corridors, the property line may be considered to be the center-
line of the public roadway or public transit corridor for the purpose of determining compliance with this section.
3. General lighting luminaires in areas such as outdoor parking, sales or storage lots shall meet these reduced ratings. Decorative luminaires located in these areas shall meet_U-
value limits for “all other outdoor lighting.”|1. IESNA Lighting Zones 0 are not applicable; refer to Lighting Zones as defined in the_California Energy Code_ and Chapter 10 of the_California Administrative Code.
2. For property lines that abut public walkways, bikeways, plazas and parking lots, the property line may be considered to be 5 feet beyond the actual property line for purpose
of determining compliance with this section. For property lines that abut public roadways and public transit corridors, the property line may be considered to be the center-
line of the public roadway or public transit corridor for the purpose of determining compliance with this section.
3. General lighting luminaires in areas such as outdoor parking, sales or storage lots shall meet these reduced ratings. Decorative luminaires located in these areas shall meet_U-
value limits for “all other outdoor lighting.”|1. IESNA Lighting Zones 0 are not applicable; refer to Lighting Zones as defined in the_California Energy Code_ and Chapter 10 of the_California Administrative Code.
2. For property lines that abut public walkways, bikeways, plazas and parking lots, the property line may be considered to be 5 feet beyond the actual property line for purpose
of determining compliance with this section. For property lines that abut public roadways and public transit corridors, the property line may be considered to be the center-
line of the public roadway or public transit corridor for the purpose of determining compliance with this section.
3. General lighting luminaires in areas such as outdoor parking, sales or storage lots shall meet these reduced ratings. Decorative luminaires located in these areas shall meet_U-
value limits for “all other outdoor lighting.”|5.106.9 Reserved.
5.106.10 Grading and paving. Construction plans shall indicate how site grading or a drainage system will manage all surface water flows to keep water from entering buildings. Examples of methods to manage surface water include, but are not limited to, the following:
Swales.
Water collection and disposal systems.
French drains.
Water retention gardens.
Other water measures which keep surface water away from buildings and aid in groundwater recharge.
Exception: Additions and alterations not altering the drainage path.
5.106.11 Reserved.
CALGreen § 4.106.2 High relevance — show source text
4.106.2 Storm water drainage and retention during construction. Projects which disturb less than one acre of soil and are not part of a larger common plan of development which in total disturbs one acre or more, shall manage storm water drainage during construction. In order to manage storm water drainage during construction, one or more of the following measures shall be implemented to prevent flooding of adjacent property, prevent erosion and retain soil runoff on the site.
Retention basins of sufficient size shall be utilized to retain storm water on the site.
Where storm water is conveyed to a public drainage system, collection point, gutter or similar disposal method, water shall be filtered by use of a barrier system, wattle or other method approved by the enforcing agency.
Compliance with a lawfully enacted storm water management ordinance.
Note: Refer to the State Water Resources Control Board for projects which disturb one acre or more of soil, or are part of a larger common plan of development which in total disturbs one acre or more of soil.
(Website: https://www.waterboards.ca.gov/water_issues/programs/stormwater/construction.html)
4.106.3 Grading and paving. Construction plans shall indicate how the site grading or drainage system will manage all surface water flows to keep water from entering buildings. Examples of methods to manage surface water include, but are not limited to, the following:
Swales
Water collection and disposal systems
French drains
Water retention gardens
Other water measures which keep surface water away from buildings and aid in groundwater recharge.
Exception: Additions and alterations not altering the drainage path.
4.106.4 Electric vehicle (EV) charging for new construction. New construction shall comply with Section 4.106.4.1 or 4.106.4.2. Electric vehicle supply equipment (EVSE) shall comply with the California Electrical Code.
Exceptions:
- On a case-by-case basis, where the local enforcing agency has determined EV charging and infrastructure are not feasible based upon one or more of the following conditions: 1.1. Where there is no local utility power supply or the local utility is unable to supply adequate power.
2025 CALIFORNIA GREEN BUILDING STANDARDS CODE 4-3
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RESIDENTIAL MANDATORY MEASURES
1.2. Where there is evidence suitable to the local enforcing agency substantiating that additional local utility infrastructure design requirements, directly related to the implementation of Section 4.106.4, may adversely impact the construction cost of the project. 2. Accessory Dwelling Units (ADU) and Junior Accessory Dwelling Units (JADU) without additional parking facilities.
CALGreen § 103.2 Medium relevance — show source text
An infill site is selected.
2. A greyfield site is selected.
3. An EPA-recognized Brownfield site is selected.||
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| |A4.103.2 Facilitate community connectivity by one of the following
methods:
1. Locate project within a1/4-mile true walking distance of at least 4
basic services;
2. Locate project within1/2-mile true walking distance of at least 7
basic services;
3. Other methods increasing access to additional resources.||
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| |Site Preservation||||||| |A4.104.1An individual with oversight responsibility for the project
has participated in an educational program promoting
environmentally friendly design or development and has provided
training or instruction to appropriate entities.||||||| |Deconstruction and Reuse of Existing Materials||||||| |A4.105.2 Existing buildings are disassembled for reuse or recycling of
building materials. The proposed structure utilizes at least one of the
following materials which can be easily reused:
1. Light fixtures
2. Plumbing fixtures
3. Doors and trim
4. Masonry
5. Electrical devices
6. Appliances
7. Foundations or portions of foundations||||||| |Site Development||||||| |4.106.2A plan is developed and implemented to manage storm water
drainage during construction.||||||| |4.106.3Construction plans shall indicate how site grading or a
drainage system will manage all surface water flows to keep water
from entering buildings.||||||| |4.106.4.1Provide capability for electric vehicle charging for one- and
two-family dwellings; townhouses with attached private garages in
accordance with Section 4.106.4.1.||||||| |4.106.4.2 Provide capability for electric vehicle charging for
multifamily dwellings and hotels/motels in accordance with Sections
4.106.4.2.2 and 4.106.4.2.6.||||||| |4.106.4.3 Provide capability for electric vehicle charging for existing
parking lots or new parking lots for existing residential buildings,CALGreen § 105.2.1 Medium relevance — show source text
A5.105.2.1 Tier 1: An alteration or addition to an existing building shall maintain at least 75 percent combined of the existing building’s primary structural elements (foundations; columns, beams, walls, and floors; and lateral elements) and existing building enclosure (roof framing, wall framing and exterior finishes). Window assemblies, insulation, portions of buildings deemed structurally unsound or hazardous, and hazardous materials that are remediated as part of the project shall not be included in the calculation.
A5.105.2.2 Tier 2: An alteration or addition to an existing building shall maintain at least 75 percent combined of the existing building’s primary structural elements (foundations; columns, beams, walls, and floors; and lateral elements) and existing building enclosure (roof framing, wall framing and exterior finishes). In addition, an alteration to an existing building shall maintain 30 percent of existing interior nonstructural elements (interior walls, doors, floor coverings, ceiling systems). Window assemblies, insulation, portions of buildings deemed structurally unsound or hazardous, and hazardous materials that are remediated as part of the project shall not be included in the calculation.
APPENDIX A5-4 2025 CALIFORNIA GREEN BUILDING STANDARDS CODE
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APPENDIX A5 — NONRESIDENTIAL VOLUNTARY MEASURES
A5.105.2.3 Verification of compliance. Documentation shall be provided in the construction documents to demonstrate compliance with Section A5.105.2.
Note: Sample Worksheet WS-6 in Chapter 8 may be used to assist in documenting compliance with this section.
A5.105.3 Deconstruction (Reserved).
SECTION A5.106—SITE DEVELOPMENT
A5.106.1 Reserved.
A5.106.2 Storm water design. Design storm water runoff rate, quantity and quality in conformance with Section A5.106.3 Low Impact Development (LID) or by local requirements, whichever are stricter.
A5.106.3 Low Impact Development (LID). All newly constructed projects shall mitigate (infiltrate, filter or treat) stormwater runoff from the 85 [th] percentile 24-hour runoff event (for volume-based BMPs) or the runoff produced by a rain event equal to two times the 85 [th] percentile hourly intensity (for flow-based BMPs) through the application of LID strategies. Employ at least two of the following methods or other best management practices to allow rainwater to soak into the ground, evaporate into the air or collect in storage receptacles for irrigation or other beneficial uses. LID strategies include, but are not limited to:
Bioretention (rain gardens)/filtration planters;
Precipitation capture (Cisterns and rain barrels);
Green roofs meeting the structural requirements of the building code;
Roof leader or impervious area disconnection;
Permeable and porous paving;
Vegetative swales and filter strips; tree preservation; and
Tree preservation and tree plantings;
Landscaping soil quality;
Stream buffer; and
Volume retention suitable for previously developed sites.
A5.106.3.1 Implementation. If applicable, coordinate LID projects with the local Regional Water Quality Control Board, which may issue a permit or otherwise require LID.
CALGreen § 105.3 Medium relevance — show source text
A5.105.3 Deconstruction (Reserved).
SECTION A5.106—SITE DEVELOPMENT
A5.106.1 Reserved.
A5.106.2 Storm water design. Design storm water runoff rate, quantity and quality in conformance with Section A5.106.3 Low Impact Development (LID) or by local requirements, whichever are stricter.
A5.106.3 Low Impact Development (LID). All newly constructed projects shall mitigate (infiltrate, filter or treat) stormwater runoff from the 85 [th] percentile 24-hour runoff event (for volume-based BMPs) or the runoff produced by a rain event equal to two times the 85 [th] percentile hourly intensity (for flow-based BMPs) through the application of LID strategies. Employ at least two of the following methods or other best management practices to allow rainwater to soak into the ground, evaporate into the air or collect in storage receptacles for irrigation or other beneficial uses. LID strategies include, but are not limited to:
Bioretention (rain gardens)/filtration planters;
Precipitation capture (Cisterns and rain barrels);
Green roofs meeting the structural requirements of the building code;
Roof leader or impervious area disconnection;
Permeable and porous paving;
Vegetative swales and filter strips; tree preservation; and
Tree preservation and tree plantings;
Landscaping soil quality;
Stream buffer; and
Volume retention suitable for previously developed sites.
A5.106.3.1 Implementation. If applicable, coordinate LID projects with the local Regional Water Quality Control Board, which may issue a permit or otherwise require LID.
Note: Further information on design of specific control measures may be found on US EPA’s website, on SWRCB’s website and from local boards that require LID.
A5.106.3.2 Greyfield or infill site. Manage 40 percent of the average annual rainfall on the site’s impervious surfaces through infiltration, reuse or evapotranspiration.
A5.106.4 Reserved.
A5.106.4.1 Reserved.
A5.106.4.2 Reserved.
A5.106.4.3 Changing rooms. For buildings with over 10 tenant-occupants, provide changing/shower facilities for tenant-occupants only in accordance with Table A5.106.4.3 or document arrangements with nearby changing/shower facilities.
Note: Additional information on recommended bicycle accommodations may be obtained from Sacramento Area Bicycle Advocates at https://sacbike.org.
TABLE A5.106.4.3 Col2 Col3 NUMBER OF
TENANT-OCCUPANTSSHOWER/CHANGING
FACILITIES REQUIRED22-TIER (12" X 15" X 72") PERSONAL
EFFECTS LOCKERS1, 2 REQUIRED0-10 0 0 11-50 1 unisex shower 2 51-100 1 unisex shower 3 101-200 1 shower stall per gender 4 Over 200 1 shower stall per gender for each
200 additional tenant-occupantsOne 2-tier locker
for each 50 additional tenant-occupants1. CALGreen § 1010.1.4 Medium relevance — show source text
Exceptions:
- Where climatic or soil conditions warrant, the slope of the ground away from the building foundation shall be permitted to be reduced to not less than 1 unit vertical in 48 units horizontal (2-percent slope).
- Impervious surfaces shall be permitted to be sloped less than 2 percent where the surface is a door landing or ramp that is required to comply with Section 1010.1.4, 1012.3 or 1012.6.1.
The procedure used to establish the final ground level adjacent to the foundation shall account for additional settlement of the backfill.
1804.4.1 [HCD 1] Construction plans. Construction plans shall indicate how the site grading or drainage system will manage all surface water flows to keep water from entering buildings in accordance with the California Green Building Standards Code (CALGreen), Chapter 4, Division 4.1.
1804.5 Grading and fill in flood hazard areas. In flood hazard areas established in Section 1612.3, grading, fill, or both, shall not be approved:
- Unless such fill is placed, compacted and sloped to minimize shifting, slumping and erosion during the rise and fall of flood water and, as applicable, wave action.
- In floodways, unless it has been demonstrated through hydrologic and hydraulic analyses performed by a registered design professional in accordance with standard engineering practice that the proposed grading or fill, or both, will not result in any increase in flood levels during the occurrence of the design flood.
- In coastal high hazard areas, unless such fill is conducted or placed to avoid diversion of water and waves toward any building or structure.
- Where design flood elevations are specified but floodways have not been designated, unless it has been demonstrated that the cumulative effect of the proposed flood hazard area encroachment, when combined with all other existing and anticipated flood hazard area encroachment, will not increase the design flood elevation more than 1 foot (305 mm) at any point.
1804.6 Compacted fill material. Where shallow foundations will bear on compacted fill material, the compacted fill shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803.
Exception: Compacted fill material 12 inches (305 mm) in depth or less need not comply with an approved report, provided that the in-place dry density is not less than 90 percent of the maximum dry density at optimum moisture content determined in accordance with ASTM D1557. The compaction shall be verified by special inspection in accordance with Section 1705.6.
1804.7 Controlled low-strength material (CLSM). Where shallow foundations will bear on controlled low-strength material (CLSM), the CLSM shall comply with the provisions of an approved geotechnical report, as set forth in Section 1803.
SECTION 1805—DAMPPROOFING AND WATERPROOFING
1805.1 General. Walls or portions thereof that retain earth and enclose interior spaces and floors below grade shall be waterproofed and dampproofed in accordance with this section, with the exception of those spaces containing groups other than residential and institutional where such omission is not detrimental to the building or occupancy.
Ventilation for crawl spaces shall comply with Section 1202.4.
CALGreen § 18-6 Medium relevance — show source text
18-6 2025 CALIFORNIA BUILDING CODE
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SOILS AND FOUNDATIONS
SECTION 1804—EXCAVATION, GRADING AND FILL
1804.1 Excavation near foundations. Excavation for any purpose shall not reduce vertical or lateral support for any foundation or adjacent foundation without first underpinning or protecting the foundation against detrimental lateral or vertical movement, or both, in accordance with Section 1803.5.7.
1804.2 Underpinning. Where underpinning is chosen to provide the protection or support of adjacent structures, the underpinning system shall be designed and installed in accordance with provisions of this chapter and Chapter 33.
1804.2.1 Underpinning sequencing. Underpinning shall be installed in a sequential manner that protects the neighboring structure and the working construction site. The sequence of installation shall be identified in the approved construction documents.
1804.3 Placement of backfill. The excavation outside the foundation shall be backfilled with soil that is free of organic material, construction debris, cobbles and boulders or with a controlled low-strength material ( CLSM ). The backfill shall be placed in lifts and compacted in a manner that does not damage the foundation or the waterproofing or dampproofing material.
Exception: CLSM need not be compacted.
1804.4 Site grading. The ground immediately adjacent to the foundation shall be sloped away from the building at a slope of not less than 1 unit vertical in 20 units horizontal (5-percent slope) for a minimum distance of 10 feet (3048 mm) measured perpendicular to the face of the wall. If physical obstructions or lot lines prohibit 10 feet (3048 mm) of horizontal distance, a 5-percent slope shall be provided to an approved alternative method of diverting water away from the foundation. Swales used for this purpose shall be sloped not less than 2 percent where located within 10 feet (3048 mm) of the building foundation. Impervious surfaces within 10 feet (3048 mm) of the building foundation shall be sloped not less than 2 percent away from the building.
Exceptions:
- Where climatic or soil conditions warrant, the slope of the ground away from the building foundation shall be permitted to be reduced to not less than 1 unit vertical in 48 units horizontal (2-percent slope).
- Impervious surfaces shall be permitted to be sloped less than 2 percent where the surface is a door landing or ramp that is required to comply with Section 1010.1.4, 1012.3 or 1012.6.1.
The procedure used to establish the final ground level adjacent to the foundation shall account for additional settlement of the backfill.
1804.4.1 [HCD 1] Construction plans. Construction plans shall indicate how the site grading or drainage system will manage all surface water flows to keep water from entering buildings in accordance with the California Green Building Standards Code (CALGreen), Chapter 4, Division 4.1.
1804.5 Grading and fill in flood hazard areas. In flood hazard areas established in Section 1612.3, grading, fill, or both, shall not be approved:
- Unless such fill is placed, compacted and sloped to minimize shifting, slumping and erosion during the rise and fall of flood water and, as applicable, wave action.
CALGreen § 105.3 Medium relevance — show source text
BENCH. A relatively level step excavated into earth material on which fill is to be placed.
COMPACTION. The densification of a fill by mechanical means.
CUT. See “Excavation.”
DOWN DRAIN. A device for collecting water from a swale or ditch located on or above a slope, and safely delivering it to an approved drainage facility.
EROSION. The wearing away of the ground surface as a result of the movement of wind, water or ice.
EXCAVATION. The removal of earth material by artificial means, also referred to as a cut.
FILL. Deposition of earth materials by artificial means.
GRADE. The vertical location of the ground surface.
GRADE, EXISTING. The grade prior to grading.
GRADE, FINISHED. The grade of the site at the conclusion of all grading efforts.
GRADING. An excavation or fill or combination thereof.
KEY. A compacted fill placed in a trench excavated in earth material beneath the toe of a slope.
SLOPE. An inclined surface, the inclination of which is expressed as a ratio of horizontal distance to vertical distance.
TERRACE. A relatively level step constructed in the face of a graded slope for drainage and maintenance purposes.
SECTION J103—PERMITS REQUIRED
J103.1 Permits required. Except as exempted in Section J103.2, grading shall not be performed without first having obtained a permit therefor from the building official. A grading permit does not include the construction of retaining walls or other structures.
J103.2 Exemptions. A grading permit shall not be required for the following:
Grading in an isolated, self-contained area, provided that the public is not endangered and that such grading will not adversely affect adjoining properties.
Excavation for construction of a structure permitted under this code.
Cemetery graves.
Refuse disposal sites controlled by other regulations.
Excavations for wells, or trenches for utilities.
APPENDIX J-2 2025 CALIFORNIA BUILDING CODE
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APPENDIX J—GRADING
- Mining, quarrying, excavating, processing or stock-piling rock, sand, gravel, aggregate or clay controlled by other regulations, provided that such operations do not affect the lateral support of, or significantly increase stresses in, soil on adjoining properties.
- Exploratory excavations performed under the direction of a registered design professional.
Exemption from the permit requirements of this appendix shall not be deemed to grant authorization for any work to be done in any manner in violation of the provisions of this code or any other laws or ordinances of this jurisdiction.
SECTION J104—PERMIT APPLICATION AND SUBMITTALS
J104.1 Submittal requirements. In addition to the provisions of Section 105.3 and 1.8.4, as applicable, the applicant shall state the estimated quantities of excavation and fill.
J104.2 Site plan requirements. In addition to the provisions of Section 107, a grading plan shall show the existing grade and finished grade in contour intervals of sufficient clarity to indicate the nature and extent of the work and show in detail that it complies with the requirements of this code. The plans shall show the existing grade on adjoining properties in sufficient detail to identify how grade changes will conform to the requirements of this code.
CALGreen § 5.106.3 Medium relevance — show source text
The NPDES permits require postconstruction runoff (post-project hydrology) to match the preconstruction runoff (pre-project hydrology) with the installation of postconstruction stormwater management measures. The NPDES permits emphasize runoff reduction through on-site stormwater use, interception, evapotranspiration and infiltration through nonstructural controls, such as Low Impact Development (LID) practices and conservation design measures. Stormwater volume that cannot be addressed using nonstructural practices is required to be captured in structural practices and be approved by the enforcing agency.
Refer to the current applicable permits on the State Water Resources Control Board website at: www.waterboards.ca.gov/constructionstormwater. Consideration to the stormwater runoff management measures should be given during the initial design process for appropriate integration into site development.
5.106.3 Reserved.
5.106.4 Bicycle parking. For buildings within the authority of California Building Standards Commission as specified in Section 103, comply with Section 5.106.4.1. For buildings within the authority of the Division of the State Architect pursuant to Section 105, comply with Section 5.106.4.2.
5.106.4.1 Bicycle parking. [BSC-CG] Comply with Sections 5.106.4.1.1 and 5.106.4.1.2; or meet the applicable local ordinance, whichever is stricter.
5.106.4.1.1 Short-term bicycle parking. If the new project or an addition or alteration is anticipated to generate visitors, provide permanently anchored bicycle racks within 200 feet of the visitors’ entrance, readily visible to passers-by, for 20 percent of the peak daily visitors, with a minimum of one two-bike capacity rack.
5.106.4.1.2 Long-term bicycle parking. Acceptable bicycle parking facility for Sections 5.106.4.1.2.1, 5.106.4.1.2.2 and 5.106.4.1.2.3 shall be conveniently located near the street and shall meet one of the following:
- Covered, lockable enclosures with permanently anchored racks for bicycles;
- Lockable bicycle rooms with permanently anchored racks; or
- Lockable, permanently anchored bicycle lockers.
Calculations for bicycle parking requirements shall be rounded up to the nearest whole number.
5.106.4.1.2.1 For new buildings with tenant spaces, provide secure bicycle parking for 10 percent of the tenant-occupants, with a minimum of one bicycle parking facility.
5.106.4.1.2.2 For additions or alterations, provide secure bicycle parking for 10 percent of the tenant-occupants being added, with a minimum of one bicycle parking facility.
5.106.4.1.2.3 For new shell buildings in phased projects, provide secure bicycle parking for 10 percent of the anticipated tenant-occupants, with a minimum of one bicycle parking facility.
5.106.4.2 Bicycle parking. [DSA-SS] For public schools and community colleges, comply with Sections 5.106.4.2.1 and 5.106.4.2.2. 5.106.4.2.1 Student bicycle parking. Provide permanently anchored bicycle racks conveniently accessed with a minimum of four two-bike capacity racks per new building.
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NONRESIDENTIAL MANDATORY MEASURES
Frequently asked questions
Must every project include infiltration features to comply with § 4.106.3?
Not necessarily. § 4.106.3 requires plans to show how surface water is kept from entering buildings; that can be accomplished by diversion, collection and disposal, or infiltration measures. Infiltration is encouraged (especially for groundwater recharge), and Appendix LID guidance calls for mitigation of the 85th‑percentile runoff using LID where applicable.
If my addition doesn’t change the drainage path, do I need to update grading plans?
If the addition or alteration does not alter the drainage path, it is excepted from the requirement in § 4.106.3. However, document that the drainage path remains unchanged to satisfy the enforcing agency.
Does CALGreen set specific rainfall depths for LID sizing?
No — § A5.106.3 sets performance targets (the 85th‑percentile 24‑hour event) but does not specify universal rainfall depths in the code text you provided. Use local rainfall statistics and local/regional stormwater guidance for numeric sizing.
Are construction‑stage BMPs required for small residential projects?
Yes — projects disturbing less than one acre (and not part of a larger plan) must still manage stormwater during construction under § 4.106.2 (retention basins, filters, wattles, or compliance with local ordinance).
Do I have to use the specific methods listed (swales, French drains, rain gardens)?
No — the code lists those methods as examples. The controlling requirement is that the plans demonstrate how all surface water flows are managed to keep water out of buildings; the listed measures are common, acceptable options. § 4.106.3.
More in California Green Building Standards Code (CALGreen)
- Administration (Chapter 1)
- Nonresidential Voluntary Measures (Appendix A5 — divisions A5.1–A5.6, electives & verification)
- Residential Mandatory Measures — Planning & Design; Energy; Water; Materials; Environmental Quality (Chapter 4)
- Definitions (Chapter 2)
- Voluntary Standards for Health Facilities (Appendix A6 / OSHPD guidance)
- Green Building – scope, mixed occupancies, phased projects (Chapter 3)
- Residential Voluntary Measures (Appendix A4 — divisions A4.1–A4.6, tiers & model ordinance)
- Nonresidential Mandatory Measures — Planning & Design; Energy; Water; Materials; Environmental Quality (Chapter 5)
- Compliance verification, construction documents & checklists (Section 102, Chapter 7, Appendix checklists)
- Referenced Organizations and Standards (Chapter 6)
- Voluntary Tiers and CALGreen Tier 1 / Tier 2 (performance tiers, thresholds)
- Installer and Special Inspector Qualifications (Chapter 7)
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